The goal of this project is to develop a rapid, low-cost method for determining regional flow in mammalian tissue. This research is based on the working hypothesis that the distribution of fluorescent microspheres injected into circulatory flow can be directly counted to determine regional blood flow. This technology would replace current indirect methods that estimate numbers of microspheres, that involve extensive handling of radioactive or caustic solutions and that require expensive instrumentation. The proposed instrument will be lower cost, rapid and will require no reagents. During Phase I, a microsphere counting instrument will be constructed to directly count fluorescent microspheres in tissue samples. The instrument and method will be tested on tissue samples containing up to four different colors of fluorescent microspheres. Design criteria for a low-cost instrument to be constructed and tested during Phase II will be established. Phase II studies will compare this instrument and methodology with the current fluorescent and radioactive methods. The instrument will provide research laboratories with an accurate, low-cost, and laborsaving method for routine measurements of regional blood flow. PROPOSED COMMERCIAL APPLICATIONS: This technology will replace current methods that estimate numbers of microspheres with instrumentation that directly counts microspheres. Potential markets include the hundreds of laboratories currently using fluorescent rnicrospheres and the large number of additional researchers utilizing the alternative radioactive and colored microsphere methods. By reducing time and cost of regional flow studies, this device will induce more researchers to correlate flow with other physiological parameters.